imagettfbbox（）在windows和linux上给出了不同的结果

i tried to use the imagettfbbox function to get the width and height for my text. after doing some work everything was fine on my linux machine. when i now run the same script on a windows machine the image looks really bad.

so i made a simple testscript and compared the result:

$e = imagettfbbox(12, 0, './Roboto-Regular.ttf', "e");

on windows i got

Array
(
 [0] => -1
 [1] => -1
 [2] => 8
 [3] => -1
 [4] => 8
 [5] => -10
 [6] => -1
 [7] => -10
)

on linux i got

Array
(
    [0] => -1
    [1] => 0
    [2] => 8
    [3] => 0
    [4] => 8
    [5] => -11
    [6] => -1
    [7] => -11
)

does anybody know i solution how to get the same values out of this command, maybe with some dirty calculation tricks?